Polymer films are often printed to display product identification, advertisement, warning, decoration, or other information. Various techniques can be used to print on the film, such as screenprinting, letterpress, offset, flexographic printing, stipple printing, laser printing, and so forth. Additionally, various types of ink can be printed. These include one and two component inks, oxidatively drying and UV-drying inks, dissolved inks, dispersed inks, and 100% ink systems.
While it may seem that many combinations of printing techniques and inks are possible, in practice, each particular type of film is printed by means of a limited number of specific printing ink/print technique combinations. For example, polyvinyl chloride (PVC) film, often used as a backing for adhesive articles, is usually directly printed using flexographic or gravure techniques and vinyl-based inks. PVC film is a desirable backing for many applications because of its durability, chemical resistance, mechanical properties, and printability. However, there are also many disadvantages to using PVC film as a backing. For example, PVC often contains high levels of plasticizer and heavy metal heat stabilizers. Additionally, PVC releases hydrochloric acid upon aging and combustion, and it may form significant quantities of dioxines under certain conditions. Due to the environmental and health concerns resulting from these features of PVC film, it is gradually being replaced by polyolefin films such as polypropylene.
For many applications, such as for the manufacture of printed adhesive tape, it is desirable to directly substitute a polyolefin film for PVC film and print the polyolefin film with the same inks as previously used. However, it has been discovered that polypropylene materials usually cannot be simply substituted for PVC. For example, while PVC film can easily be directly printed, it is more difficult to directly print onto a polyolefin film.
For many adhesive tape printing applications it is further desirable that the tape be capable of being unwound at high speed without producing a level of noise which may damage the heating of the operators using the tape, either in a printing or use step. Consequently, when replacing PVC film with polyolefin film as the backing, it is desirable to duplicate both the quiet unwind and printable characteristics of the PVC film.
Several coatings have been disclosed which are said to provide a printable and/or low noise olefinic polymer film. For example, U.S. Pat. No. 3,676,391 discloses a coating composition for priming untreated polyolefin substrates which comprises a resin of chlorinated polyolefin and ethylene/vinyl acetate copolymer. This patent further discloses a backsize for pressure sensitive adhesive tape which is a blend of cellulose acetate butyrate and copolyester and/or acrylate copolymer. The backsize is said to be both printable and more easily unwound. U.S. Pat. No. 4,070,523 discloses a printable release coating for flexible pressure sensitive tape which incorporates polyketone resins blended with a release agent and an elastomeric or resinous film. U.S. Pat. No. 4,587,156 discloses a directly printable backsize coating composition for PSA tape comprising a ternary mixture of a low adhesion backsize compound, an ink anchoring resin, and a primer resin wherein the surface free energy of the ink anchoring resin and the primer are within about ten percent of the surface free energy of the low adhesion backsize compound. U.S. Pat. No. 4,599,260 discloses a directly printable tape having a backsize coating comprising a mixture of a low adhesion backsize compound, such as a polyvinyl carbamate polymer, and an ink adhesion promoter, such as a chlorinated polyolefin. Also disclosed is an ink composition comprising a conventional flexographic ink composition in conjunction with an effective amount of a chlorinated polyolefin.
U.S. Pat. No. 4,708,907 discloses a writable adhesive tape having a polyolefin substrate, an adhesive layer on one side of the substrate, and a writable anti-adhesive layer on the opposite side. The anti-adhesive layer comprises a blend of 25-55% by weight of a chlorinated polyolefin, 20-50% of a polyaldehyde resin, 5-20% of an anti-adhesive agent, and 5-25% of a matting charge.
U.S. Pat. No. 5,168,002 discloses a pressure sensitive self-adhesive tape including an olefinic polymer substrate, a pressure sensitive adhesive on one face of the substrate, and a non-stick layer on the opposite face. The non-stick layer is composed of a blend of a chlorinated olefinic resin, an acrylic resin, and a non-stick agent. Similarly, a blend of a chlorinated olefinic resin and an acrylic resin has been used commercially on polypropylene backing in the manufacture of a low noise directly printable adhesive packaging tape. While both coatings provide olefinic films with the low noise and printability desired in a PVC replacement, the blends tend to phase separate with time, especially at higher levels of the chlorinated olefinic resin, and require additional precautions to prevent the formation of an inhomogeneous coating. Such inhomogeneous coatings exhibit reduced printability and increased unwind release values.